1. Field of the Invention
The present invention relates to a light illuminating unit, and more particularly, to a light illuminating unit for processing of an alignment layer of a liquid crystal display (LCD) device, and a manufacturing method thereof.
2. Discussion of the Related Art
A typical LCD device includes two substrates each having electrodes on one surface. The two substrates are arranged such that the surfaces on which the electrodes are formed face each other, and a liquid crystal layer is interposed between the two substrates. A LCD device having the described construction displays an image by varying the alignment of molecules of the liquid crystal layer using an electric field generated by a voltage applied to the two substrates. As the electric field is varied the alignment of the liquid crystal molecules changes, changing the light transmittance of the liquid crystal layer in correspondence with the applied voltage to generate an image.
A typical LCD device includes a liquid crystal (LC) panel for displaying an image and a driving unit for applying a driving signal to the LC panel. The first and second substrates of the LC panel are bonded together with a predetermined intervening space between the two substrates, and with an LC layer interposed between the two substrates.
LCD devices may be of various types. In an in-plane switching (ISP) mode LCD device the first substrate includes a plurality of gate lines separated by a constant interval in a first direction; a plurality of data lines separated by a constant interval and arranged in a perpendicular direction to the gate lines; pixel electrodes formed in a comb shape having a plurality of teeth in the pixel regions defined by the gate lines and the data lines crossing each other; a common electrode alternately formed with the teeth of the pixel electrodes; and a plurality of thin film transistors (TFTs) to be switched in response to a signal from the gate lines to transfer signals of the data lines to the pixel electrodes.
The second substrate includes a black matrix layer for blocking light passing through portions other than the pixel regions, and a color filter layer for realizing colors.
An alignment layer is formed on each of the first and second substrates. The alignment layer is processed to provide an initial alignment direction for the molecules of the liquid crystal layer of the LCD device.
The alignment methods of the related art for processing the alignment layer include a rubbing method.
In the rubbing method, an alignment material such as polyimide (PI) is coated on a substrate, and mechanical friction is generated using a rubbing cloth to generate fine grooves in the alignment material to induce an alignment direction. The rubbing method is widely used in the industry because it can be applied over large areas at a high speed.
However, the shape of the grooves formed in the alignment layer changes with variations in the amount of friction generated during the rubbing process. The variations in the shape of the grooves may result in inhomogeneous alignment of liquid crystal molecules of the liquid crystal layer. Irregular phase distortion and light scattering due to the inhomogeneous alignment of the liquid crystal molecules may reduce the performance of an LCD device.
In addition, dusts and static electricity generated during rubbing processes reduce the manufacturing yield for the resulting LCD devices.
Various methods for manufacturing a liquid crystal alignment layer without the use of physical contact are being studied in order to solve the problems of the rubbing method. Among the studied methods are included techniques using photo-alignment technology. In the photo-alignment technology, a liquid crystal alignment layer is processed by illuminating polarized ultraviolet (UV) light onto a polymer film.
In contrast to the rubbing method, alignment methods using photo-alignment technology do not generate dusts and static electricity and can avoid the yield reduction caused by dust and static electricity. In addition, by allowing the liquid crystal molecules to be uniformly arranged over an entire surface of an alignment layer and the uniformity of the alignment of the liquid crystal layer can be improved, and phase distortion or light scattering problems can be eliminated or reduced.
FIG. 1 is a schematic diagram illustrating an alignment process of a liquid crystal alignment layer according to a related art rubbing process.
Referring to FIG. 1, according to the related art rubbing process, a polymer compound such as polyimide or the like is coated on a substrate 2. Thereafter, a rubbing drum 7 rotates at a high speed to rub the surface of the coated substrate 2 so that microgrooves are formed on the surface of the polymer compound. Herein, the rubbing drum 7 is rolled up in a predetermined cloth with nylon or polyester rayon.
Through the rubbing process, the liquid crystal molecules are aligned at a predetermined pretilt angle on the surface of the alignment agent. Meanwhile, since the rubbing process has is simple and adaptive for scaling up the size of device and usable in high-speed production, it is widely used industrially.
However, the microgrooves formed in the alignment layer may have non-uniform shapes depending on the amount of frictional force between the cloth and the alignment layer 1 during rubbing. As a result, the alignment of the liquid crystal molecules can be non-uniform resulting in phase distortion and light scattering. Moreover, the substrate 2 may be damaged due to electrostatic discharge (ESD) generated while rubbing the surface of the polymer. Further, there is a problem that a production yield decreases due to the micro dust generated from the rubbing drum 7.